U.S. patent number 10,952,249 [Application Number 16/325,917] was granted by the patent office on 2021-03-16 for method for transmitting uplink signal through multiple unlicensed component carriers in wireless communication system supporting unlicensed band, and device supporting same.
This patent grant is currently assigned to LG Electronics Inc.. The grantee listed for this patent is LG Electronics Inc.. Invention is credited to Joonkui Ahn, Seonwook Kim.
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United States Patent |
10,952,249 |
Kim , et al. |
March 16, 2021 |
Method for transmitting uplink signal through multiple unlicensed
component carriers in wireless communication system supporting
unlicensed band, and device supporting same
Abstract
The present invention provides a method for transmitting an
uplink signal to a base station by a terminal in a wireless
communication system supporting an unlicensed band, and a device
supporting the same. More particularly, the present invention
provides a method for transmitting an uplink signal through an LBT
method of a terminal and a plurality of unlicensed component
carriers on the basis of the LBT method when two or more unlicensed
component carriers among the plurality of unlicensed component
carriers are included in different timing advance groups (TAGs) in
a wireless communication system supporting the plurality of
unlicensed component carriers, and a device supporting the
same.
Inventors: |
Kim; Seonwook (Seoul,
KR), Ahn; Joonkui (Seoul, KR) |
Applicant: |
Name |
City |
State |
Country |
Type |
LG Electronics Inc. |
Seoul |
N/A |
KR |
|
|
Assignee: |
LG Electronics Inc. (Seoul,
KR)
|
Family
ID: |
1000005427625 |
Appl.
No.: |
16/325,917 |
Filed: |
August 16, 2017 |
PCT
Filed: |
August 16, 2017 |
PCT No.: |
PCT/KR2017/008879 |
371(c)(1),(2),(4) Date: |
February 15, 2019 |
PCT
Pub. No.: |
WO2018/034485 |
PCT
Pub. Date: |
February 22, 2018 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20190191459 A1 |
Jun 20, 2019 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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62376410 |
Aug 18, 2016 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04W
74/00 (20130101); H04W 16/14 (20130101); H04W
74/08 (20130101); H04W 74/0808 (20130101); H04W
72/1268 (20130101); H04W 84/045 (20130101) |
Current International
Class: |
H04W
16/14 (20090101); H04W 74/00 (20090101); H04W
74/08 (20090101); H04W 72/12 (20090101); H04W
84/04 (20090101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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WO2015179055 |
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Nov 2015 |
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WO |
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WO2016021958 |
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Feb 2016 |
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WO |
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WO2016072685 |
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May 2016 |
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WO |
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WO2016085295 |
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Jun 2016 |
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WO |
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WO2016122110 |
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Aug 2016 |
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WO |
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Other References
PCT International Search Report and Written Opinion in
International Application No. PCT/KR2017/008879, dated Dec. 7,
2017, 20 pages (with English translation). cited by applicant .
Extended European Search Report in European Application No.
17841667.3, dated Mar. 6, 2020, 13 pages. cited by applicant .
Samsung, "Discussion on UL transmission for LAA," R1-152872, 3GPP
TSG RAN WG1 Meeting #81, Fukuoka, Japan, dated May 25-29, 2015, 5
pages, XP050973756. cited by applicant.
|
Primary Examiner: Jeong; Moo
Attorney, Agent or Firm: Fish & Richardson P.C.
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a National Stage application under 35 U.S.C.
.sctn. 371 of International Application No. PCT/KR2017/008879,
filed on Aug. 16, 2017, which claims the benefit of U.S.
Provisional Application No. 62/376,410, filed on Aug. 18, 2016. The
disclosures of the prior applications are incorporated by reference
in their entirety.
Claims
What is claimed is:
1. A method for transmitting an uplink signal on a plurality of
unlicensed Component Carriers (CCs) belonging to different Timing
Advance Groups (TAGs) by a user equipment (UE) in a wireless
communication system supporting an unlicensed band, the method
comprising: determining a start point of a subframe that is
earliest in a time domain from a specific timing among subframes on
the plurality of the unlicensed CCs as a first transmission start
point; performing a first channel access procedure on the plurality
of the unlicensed CCs based on the first transmission start point;
and based on a result of the first channel access procedure,
performing an uplink signal transmission on the plurality of the
unlicensed CCs from the first transmission start point, or
performing a second channel access procedure for the uplink signal
transmission based on a second transmission start point, wherein
the second channel access procedure is different from the first
channel access procedure, and the second transmission start point
is different from the first transmission start point.
2. The method of claim 1, wherein the specific timing comprises: a
timing at which the UE attempts the uplink signal transmission, or
a timing at which the UE fails a channel access procedure performed
in advance for the uplink signal transmission.
3. The method of claim 1, wherein the first channel access
procedure and the second channel access procedure comprise Listen
Before Talk (LBT) for the plurality of the unlicensed CCs.
4. The method of claim 1, wherein the UE performs the uplink signal
transmission on the plurality of the unlicensed CCs from the first
transmission start point based on a success of the first channel
access procedure.
5. The method of claim 1, the performing the uplink signal
transmission on the plurality of the unlicensed CCs, comprising:
transmitting an initial signal from the first transmission start
point to a start point of a subframe on each of the plurality of
the unlicensed CCs; and transmitting the uplink signal from the
start point of the subframe on each of the plurality of the
unlicensed CC after the first transmission start point.
6. The method of claim 5, wherein the initial signal comprises: a
signal configured in advance on a system, or a portion or whole of
the uplink signal to be transmitted after the initial signal.
7. The method of claim 1, wherein the UE performs the second
channel access procedure for the uplink signal transmission based
on a failure of the first channel access procedure.
8. The method of claim 1, performing the second channel access
procedure comprising: determining a start point of the subframe
that is earliest in the time domain after the first transmission
start point among subframes on the plurality of the unlicensed CCs
as the second transmission start point; and performing the second
channel access procedure on the plurality of the unlicensed CCs
based on the second transmission start point.
9. The method of claim 1, wherein the UE is connected to the
plurality of the unlicensed CCs by a dual connectivity.
10. A user equipment (UE) configured to transmit an uplink signal
on a plurality of unlicensed Component Carriers (CCs) belonging to
different Timing Advance Groups (TAGs) in a wireless communication
system supporting an unlicensed band, the UE comprising: a
transmitter; a receiver; and a processor configured to operate by
being connected to the transmitter and the receiver, wherein the
processor is further configured to: determine a start point of a
subframe that is earliest in a time domain from a specific timing
among subframes on the plurality of the unlicensed CCs as a first
transmission start point; perform a first channel access procedure
on the plurality of the unlicensed CCs based on the first
transmission start point; and based on a result of the first
channel access procedure, perform an uplink signal transmission on
the plurality of the unlicensed CCs from the first transmission
start point, or perform a second channel access procedure for the
uplink signal transmission based on a second transmission start
point, wherein the second channel access procedure is different
from the first channel access procedure, and the second
transmission start point is different from the first transmission
start point.
11. The UE of claim 10, wherein the specific timing comprises: a
timing at which the UE attempts the uplink signal transmission, or
a timing at which the UE fails a channel access procedure performed
in advance for the uplink signal transmission.
12. The UE of claim 10, wherein the first channel access procedure
and the second channel access procedure comprise Listen Before Talk
(LBT) for the plurality of the unlicensed CCs.
13. The UE of claim 10, wherein the UE performs the uplink signal
transmission on the plurality of the unlicensed CCs from the first
transmission start point based on a success of the first channel
access procedure.
14. The UE of claim 10, wherein performing the uplink signal
transmission on the plurality of the unlicensed CCs comprises:
transmitting an initial signal from the first transmission start
point to a start point of a subframe on each of the plurality of
the unlicensed CCs; and transmitting the uplink signal from the
start point of the subframe on each of the plurality of the
unlicensed CC after the first transmission start point.
15. The UE of claim 14, wherein the initial signal comprises: a
signal configured in advance on a system, or a portion or whole of
the uplink signal to be transmitted after the initial signal.
16. The UE of claim 10, wherein the UE is configured to perform the
second channel access procedure for the uplink signal transmission
based on a failure of the first channel access procedure.
17. The UE of claim 10, wherein performing the second channel
access procedure comprises: determining a start point of the
subframe that is earliest in the time domain after the first
transmission start point among subframes on the plurality of the
unlicensed CCs as the second transmission start point; and
performing the second channel access procedure on the plurality of
the unlicensed CCs based on the second transmission start
point.
18. The UE of claim 10, wherein the UE is configured to connect to
the plurality of the unlicensed CCs by a dual connectivity.
19. A processing apparatus configured to control a user equipment
(UE) to transmit an uplink signal on a plurality of unlicensed
Component Carriers (CCs) belonging to different Timing Advance
Groups (TAGs) in a wireless communication system supporting an
unlicensed band, the processing apparatus comprising: at least
processor; and at least one computer memory operably connected to
the at least one processor and storing instructions that, based on
being executed by the at least one processor, perform operations
comprising: determining a start point of a subframe that is
earliest in a time domain from a specific timing among subframes on
the plurality of the unlicensed CCs as a first transmission start
point; performing a first channel access procedure on the plurality
of the unlicensed CCs based on the first transmission start point;
and based on a result of the first channel access procedure,
performing an uplink signal transmission on the plurality of the
unlicensed CCs from the first transmission start point, or
performing a second channel access procedure for the uplink signal
transmission based on a second transmission start point, wherein
the second channel access procedure is different from the first
channel access procedure, and the second transmission start point
is different from the first transmission start point.
Description
TECHNICAL FIELD
The following description relates to a wireless communication
system, and more particularly, to a method of transmitting an
uplink signal to a base station by a user equipment in a wireless
communication system supportive of an unlicensed band and apparatus
supporting the same.
Particularly, if two or more unlicensed component carriers among a
plurality of unlicensed component carriers in a wireless
communication system supportive of a plurality of the unlicensed
component carriers are included in different Timing Advance Groups
(TAGs), the following description relates to an LBT method of a
user equipment, uplink signal transmitting method through a
plurality of unlicensed component carriers based thereon, and
apparatus supporting the same.
BACKGROUND ART
Wireless access systems have been widely deployed to provide
various types of communication services such as voice or data. In
general, a wireless access system is a multiple access system that
supports communication of multiple users by sharing available
system resources (a bandwidth, transmission power, etc.) among
them. For example, multiple access systems include a Code Division
Multiple Access (CDMA) system, a Frequency Division Multiple Access
(FDMA) system, a Time Division Multiple Access (TDMA) system, an
Orthogonal Frequency Division Multiple Access (OFDMA) system, and a
Single Carrier Frequency Division Multiple Access (SC-FDMA)
system.
As more communication devices require larger communication
capacities, the demand for a proposal of an operation of each
communication device on a contention-based accessible unlicensed
band is rising.
At the same time, necessity for mobile broadband communication
improved better than the existing Radio Access Technology (RAT) is
on the rise as well. Moreover, the next generation communication
also considers massive Machine Type Communications (MTC) providing
various services anywhere and at any time by connecting a multitude
of devise and things together. Besides, a communication system
design in consideration of a service/UE sensitive to reliability
and latency is taken into consideration.
As described above, the introduction of the next generation RAT
considering the enhanced mobile broadband communication, massive
MTC, Ultra-reliable and low latency communication (URLLC), and the
like has been discussed.
DISCLOSURE OF THE INVENTION
Technical Task
One technical task of the present invention is to provide a method
of transmitting an uplink signal in a wireless communication system
supportive of an unlicensed band and apparatus therefor.
Particularly, in case that a plurality of unlicensed component
carriers are connected to a single user equipment by dual
connectivity, the technical task of the present invention is to
provide a channel access procedure of the user equipment (e.g.,
Listen Before Talk (LBT) method), Physical Downlink Control Channel
(PDCCH) search space configuring method, and apparatus
therefor.
It will be appreciated by persons skilled in the art that the
objects that could be achieved with the present disclosure are not
limited to what has been particularly described hereinabove and the
above and other objects that the present disclosure could achieve
will be more clearly understood from the following detailed
description.
Technical Solutions
The present invention provides a method of transmitting an uplink
signal to a base station by a user equipment in a wireless
communication system supportive of an unlicensed band and apparatus
therefor.
In one technical aspect of the present invention, provided herein
is a method of transmitting an uplink signal through a plurality of
unlicensed Component Carriers (CCs) including two or more
unlicensed CCs belonging to different Timing Advance Groups (TAGs)
by a user equipment in-a wireless communication system supportive
of an unlicensed band, the method including determining a start
point of a foremost subframe in a time domain with reference to a
specific timing among subframes on a plurality of the unlicensed
CCs as a transmission start point, performing a channel access
procedure on a plurality of the unlicensed CCs with reference to
the transmission start point, and depending on a success or failure
of the channel access procedure, performing an uplink signal
transmission on the plurality of the unlicensed CCs from the
transmission start point or attempting the uplink signal
transmission by determining a new transmission start point and
performing a new channel access procedure with reference to the new
transmission start point.
In another technical aspect of the present invention, provided
herein is a user equipment in transmitting an uplink signal through
a plurality of unlicensed Component Carriers (CCs) including two or
more unlicensed CCs belonging to different Timing Advance Groups
(TAGs) in a wireless communication system supportive of an
unlicensed band, the user equipment including a transmitter, a
receiver, and a processor configured to operate by being connected
to the transmitter and the receiver, wherein the processor is
further configured to determine a start point of a foremost
subframe in a time domain with reference to a specific timing among
subframes on a plurality of the unlicensed CCs as a transmission
start point, perform a channel access procedure on a plurality of
the unlicensed CCs with reference to the transmission start point,
and depending on a success or failure of the channel access
procedure, perform an uplink signal transmission on the plurality
of the unlicensed CCs from the transmission start point or attempt
the uplink signal transmission by determining a new transmission
start point and performing a new channel access procedure with
reference to the new transmission start point.
Preferably, the specific timing may include a timing for the user
equipment to attempt an uplink signal transmission scheduled on the
plurality of the unlicensed CCs or a timing for the user equipment
to fail in the channel access procedure performed in advance for
the uplink signal transmission scheduled on the plurality of the
unlicensed CCs.
Preferably, the channel access procedure may include Listen Before
Talk (LBT) for the plurality of the unlicensed CCs.
Preferably, if succeeding in the channel access procedure, the user
equipment may perform the uplink signal transmission on the
plurality of the unlicensed CCs from the transmission start
point.
More preferably, the performing by the user equipment the uplink
signal transmission on the plurality of the unlicensed CCs may
include transmitting an initial signal from the transmission start
point to a start point of a subframe per unlicensed CC and
transmitting the uplink signal scheduled per unlicensed CC from the
start point of the subframe per unlicensed CC after the
transmission start point.
Here, the initial signal may include a signal configured in advance
on a system or a portion or whole of the uplink signal to be
transmitted thereafter.
Preferably, if failing in the channel access procedure, the user
equipment may attempt the uplink signal transmission by determining
the new transmission start point and performing the channel access
procedure with reference to the new transmission start point.
More preferably, the attempting by the user equipment the uplink
signal transmission by determining the new transmission start point
and performing the channel access procedure with reference to the
new transmission start point may further include determining a
start point of a foremost subframe in the time domain with
reference to a timing after the transmission start point among
subframes on a plurality of the unlicensed CCs as the new
transmission start point; and attempting the uplink signal
transmission by performing the new channel access procedure on the
plurality of the unlicensed CCs with reference to the new
transmission start point.
Preferably, the user equipment may be connected to the two or more
unlicensed CCs on a manner of a dual connectivity.
It is to be understood that both the foregoing general description
and the following detailed description of the present disclosure
are exemplary and explanatory and are intended to provide further
explanation of the disclosure as claimed.
Advantageous Effects
As is apparent from the above description, the embodiments of the
present invention have the following effects.
According to the present invention, although a plurality of
unlicensed component carriers are connected through nonideal
backhaul, a user equipment performs a more efficient channel access
procedure on a plurality of the unlicensed component carriers and
is then able to perform an uplink signal transmission based on
it.
Particularly, according to the present invention, in case that a
plurality of unlicensed component carriers belonging to different
TAGs exist, a signal transmission blocking effect in another
U-cell, which is caused to a plurality of the unlicensed component
carriers due to different UL timings, can be prevented.
It will be appreciated by persons skilled in the art that the
effects that can be achieved with the present disclosure are not
limited to what has been particularly described hereinabove and
other advantages of the present disclosure will be more clearly
understood from the following detailed description taken in
conjunction with the accompanying drawings.
DESCRIPTION OF DRAWINGS
The accompanying drawings, which are included to provide a further
understanding of the invention, provide embodiments of the present
invention together with detail explanation. Yet, a technical
characteristic of the present invention is not limited to a
specific drawing. Characteristics disclosed in each of the drawings
are combined with each other to configure a new embodiment.
Reference numerals in each drawing correspond to structural
elements.
FIG. 1 is a diagram illustrating physical channels and a signal
transmission method using the physical channels.
FIG. 2 is a diagram illustrating exemplary radio frame
structures.
FIG. 3 is a diagram illustrating an exemplary resource grid for the
duration of a downlink slot.
FIG. 4 is a diagram illustrating an exemplary structure of an
uplink subframe.
FIG. 5 is a diagram illustrating an exemplary structure of a
downlink subframe.
FIG. 6 is a diagram to describe the concept of dual connectivity
usable for the present invention.
FIG. 7 is a diagram illustrating an exemplary carrier aggregation
(CA) environment supported in a long term evolution-unlicensed
(LTE-U) system;
FIG. 8 is a diagram illustrating an exemplary frame based equipment
(FBE) operation as one of listen-before-talk (LBT) operations.
FIG. 9 is a block diagram illustrating the FBE operation.
FIG. 10 is a diagram illustrating an exemplary load based equipment
(LBE) operation as one of the LBT operations.
FIG. 11 is a diagram illustrating methods of transmitting a
discovery reference signal (DRS) supported in a licensed assisted
access (LAA) system.
FIG. 12 is a diagram illustrating a channel access procedure (CAP)
and contention window adjustment (CWA).
FIG. 13 is a diagram illustrating a partial transmission time
interval (TTI) or a partial subframe, which is applicable to the
present invention.
FIG. 14 is a diagram showing a self-contained subframe structure
applicable to the present invention.
FIG. 15 and FIG. 16 are diagrams showing representative
connectivity schemes of TXRU and antenna element.
FIG. 17 and FIG. 18 are diagrams showing dual connectivity
configurations including unlicensed component carriers applicable
to the present invention.
FIG. 19 is a diagram schematically showing a subframe structure per
cell in aspect of a specific UE for two cells belonging to
different TAGs.
FIG. 20 is a diagram schematically showing a case that a boundary
of DL/UL subframe structure for different cells is not aligned.
FIG. 21 is a diagram showing configuration of a UE and base station
for implementing the proposed embodiments.
FIG. 22 is a diagram illustrating configurations of a UE and a base
station capable of being implemented by the embodiments proposed in
the present invention.
BEST MODE FOR INVENTION
The embodiments of the present disclosure described below are
combinations of elements and features of the present disclosure in
specific forms. The elements or features may be considered
selective unless otherwise mentioned. Each element or feature may
be practiced without being combined with other elements or
features. Further, an embodiment of the present disclosure may be
constructed by combining parts of the elements and/or features.
Operation orders described in embodiments of the present disclosure
may be rearranged. Some constructions or elements of any one
embodiment may be included in another embodiment and may be
replaced with corresponding constructions or features of another
embodiment.
In the description of the attached drawings, a detailed description
of known procedures or steps of the present disclosure will be
avoided lest it should obscure the subject matter of the present
disclosure. In addition, procedures or steps that could be
understood to those skilled in the art will not be described
either.
Throughout the specification, when a certain portion "includes" or
"comprises" a certain component, this indicates that other
components are not excluded and may be further included unless
otherwise noted. The terms "unit", "-or/er" and "module" described
in the specification indicate a unit for processing at least one
function or operation, which may be implemented by hardware,
software or a combination thereof. In addition, the terms "a or
an", "one", "the" etc. may include a singular representation and a
plural representation in the context of the present disclosure
(more particularly, in the context of the following claims) unless
indicated otherwise in the specification or unless context clearly
indicates otherwise.
In the embodiments of the present disclosure, a description is
mainly made of a data transmission and reception relationship
between a Base Station (BS) and a User Equipment (UE). A BS refers
to a terminal node of a network, which directly communicates with a
UE. A specific operation described as being performed by the BS may
be performed by an upper node of the BS.
Namely, it is apparent that, in a network comprised of a plurality
of network nodes including a BS, various operations performed for
communication with a UE may be performed by the BS, or network
nodes other than the BS. The term `BS` may be replaced with a fixed
station, a Node B, an evolved Node B (eNode B or eNB), an Advanced
Base Station (ABS), an access point, etc.
In the embodiments of the present disclosure, the term terminal may
be replaced with a UE, a Mobile Station (MS), a Subscriber Station
(SS), a Mobile Subscriber Station (MSS), a mobile terminal, an
Advanced Mobile Station (AMS), etc.
A transmission end is a fixed and/or mobile node that provides a
data service or a voice service and a reception end is a fixed
and/or mobile node that receives a data service or a voice service.
Therefore, a UE may serve as a transmission end and a BS may serve
as a reception end, on an UpLink (UL). Likewise, the UE may serve
as a reception end and the BS may serve as a transmission end, on a
DownLink (DL).
The embodiments of the present disclosure may be supported by
standard specifications disclosed for at least one of wireless
access systems including an Institute of Electrical and Electronics
Engineers (IEEE) 802.xx system, a 3rd Generation Partnership
Project (3GPP) system, a 3GPP Long Term Evolution (LTE) system, and
a 3GPP2 system. In particular, the embodiments of the present
disclosure may be supported by the standard specifications, 3GPP TS
36.211, 3GPP TS 36.212, 3GPP TS 36.213, 3GPP TS 36.321 and 3GPP TS
36.331. That is, the steps or parts, which are not described to
clearly reveal the technical idea of the present disclosure, in the
embodiments of the present disclosure may be explained by the above
standard specifications. All terms used in the embodiments of the
present disclosure may be explained by the standard
specifications.
Reference will now be made in detail to the embodiments of the
present disclosure with reference to the accompanying drawings. The
detailed description, which will be given below with reference to
the accompanying drawings, is intended to explain exemplary
embodiments of the present disclosure, rather than to show the only
embodiments that can be implemented according to the
disclosure.
The following detailed description includes specific terms in order
to provide a thorough understanding of the present disclosure.
However, it will be apparent to those skilled in the art that the
specific terms may be replaced with other terms without departing
the technical spirit and scope of the present disclosure.
For example, the term, TxOP may be used interchangeably with
transmission period or Reserved Resource Period (RRP) in the same
sense. Further, a Listen-Before-Talk (LBT) procedure may be
performed for the same purpose as a carrier sensing procedure for
determining whether a channel state is idle or busy, CCA (Clear
Channel Assessment), CAP (Channel Access Procedure).
Hereinafter, 3GPP LTE/LTE-A systems are explained, which are
examples of wireless access systems.
The embodiments of the present disclosure can be applied to various
wireless access systems such as Code Division Multiple Access
(CDMA), Frequency Division Multiple Access (FDMA), Time Division
Multiple Access (TDMA), Orthogonal Frequency Division Multiple
Access (OFDMA), Single Carrier Frequency Division Multiple Access
(SC-FDMA), etc.
CDMA may be implemented as a radio technology such as Universal
Terrestrial Radio Access (UTRA) or CDMA2000. TDMA may be
implemented as a radio technology such as Global System for Mobile
communications (GSM)/General packet Radio Service (GPRS)/Enhanced
Data Rates for GSM Evolution (EDGE). OFDMA may be implemented as a
radio technology such as IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX),
IEEE 802.20, Evolved UTRA (E-UTRA), etc.
UTRA is a part of Universal Mobile Telecommunications System
(UMTS). 3GPP LTE is a part of Evolved UMTS (E-UMTS) using E-UTRA,
adopting OFDMA for DL and SC-FDMA for UL. LTE-Advanced (LTE-A) is
an evolution of 3GPP LTE. While the embodiments of the present
disclosure are described in the context of a 3GPP LTE/LTE-A system
in order to clarify the technical features of the present
disclosure, the present disclosure is also applicable to an IEEE
802.16e/m system, etc.
1. 3GPP LTE/LTE-A System
1.1. Physical Channels & Signal Transceiving Method Using the
Same
In a wireless access system, a UE receives information from an eNB
on a DL and transmits information to the eNB on a UL. The
information transmitted and received between the UE and the eNB
includes general data information and various types of control
information. There are many physical channels according to the
types/usages of information transmitted and received between the
eNB and the UE.
FIG. 1 illustrates physical channels and a general signal
transmission method using the physical channels, which may be used
in embodiments of the present disclosure.
When a UE is powered on or enters a new cell, the UE performs
initial cell search (S11). The initial cell search involves
acquisition of synchronization to an eNB. Specifically, the UE
synchronizes its timing to the eNB and acquires information such as
a cell Identifier (ID) by receiving a Primary Synchronization
Channel (P-SCH) and a Secondary Synchronization Channel (S-SCH)
from the eNB.
Then the UE may acquire information broadcast in the cell by
receiving a Physical Broadcast Channel (PBCH) from the eNB.
During the initial cell search, the UE may monitor a DL channel
state by receiving a Downlink Reference Signal (DL RS).
After the initial cell search, the UE may acquire more detailed
system information by receiving a Physical Downlink Control Channel
(PDCCH) and receiving a Physical Downlink Shared Channel (PDSCH)
based on information of the PDCCH (S12).
To complete connection to the eNB, the UE may perform a random
access procedure with the eNB (S13 to S16). In the random access
procedure, the UE may transmit a preamble on a Physical Random
Access Channel (PRACH) (S13) and may receive a PDCCH and a PDSCH
associated with the PDCCH (S14). In the case of contention-based
random access, the UE may additionally perform a contention
resolution procedure including transmission of an additional PRACH
(S15) and reception of a PDCCH signal and a PDSCH signal
corresponding to the PDCCH signal (S16).
After the above procedure, the UE may receive a PDCCH and/or a
PDSCH from the eNB (S17) and transmit a Physical Uplink Shared
Channel (PUSCH) and/or a Physical Uplink Control Channel (PUCCH) to
the eNB (S18), in a general UL/DL signal transmission
procedure.
Control information that the UE transmits to the eNB is generically
called Uplink Control Information (UCI). The UCI includes a Hybrid
Automatic Repeat and reQuest Acknowledgement/Negative
Acknowledgement (HARQ-ACK/NACK), a Scheduling Request (SR), a
Channel Quality Indicator (CQI), a Precoding Matrix Index (PMI), a
Rank Indicator (RI), etc.
In the LTE system, UCI is generally transmitted on a PUCCH
periodically. However, if control information and traffic data
should be transmitted simultaneously, the control information and
traffic data may be transmitted on a PUSCH. In addition, the UCI
may be transmitted aperiodically on the PUSCH, upon receipt of a
request/command from a network.
1.2. Resource Structure
FIG. 2 illustrates exemplary radio frame structures used in
embodiments of the present disclosure.
FIG. 2(a) illustrates frame structure type 1. Frame structure type
1 is applicable to both a full Frequency Division Duplex (FDD)
system and a half FDD system.
One radio frame is 10 ms (Tf=307200 Ts) long, including equal-sized
20 slots indexed from 0 to 19. Each slot is 0.5 ms (Tslot=15360 Ts)
long. One subframe includes two successive slots. An ith subframe
includes 2ith and (2i+1)th slots. That is, a radio frame includes
10 subframes. A time required for transmitting one subframe is
defined as a Transmission Time Interval (TTI). Ts is a sampling
time given as Ts=1/(15 kHz.times.2048)=3.2552.times.10-8 (about 33
ns). One slot includes a plurality of Orthogonal Frequency Division
Multiplexing (OFDM) symbols or SC-FDMA symbols in the time domain
by a plurality of Resource Blocks (RBs) in the frequency
domain.
A slot includes a plurality of OFDM symbols in the time domain.
Since OFDMA is adopted for DL in the 3GPP LTE system, one OFDM
symbol represents one symbol period. An OFDM symbol may be called
an SC-FDMA symbol or symbol period. An RB is a resource allocation
unit including a plurality of contiguous subcarriers in one
slot.
In a full FDD system, each of 10 subframes may be used
simultaneously for DL transmission and UL transmission during a
10-ms duration. The DL transmission and the UL transmission are
distinguished by frequency. On the other hand, a UE cannot perform
transmission and reception simultaneously in a half FDD system.
The above radio frame structure is purely exemplary. Thus, the
number of subframes in a radio frame, the number of slots in a
subframe, and the number of OFDM symbols in a slot may be
changed.
FIG. 2(b) illustrates frame structure type 2. Frame structure type
2 is applied to a Time Division Duplex (TDD) system. One radio
frame is 10 ms (Tf=307200Ts) long, including two half-frames each
having a length of 5 ms (=153600Ts) long. Each half-frame includes
five subframes each being 1 ms (=30720Ts) long. An ith subframe
includes 2ith and (2i+1)th slots each having a length of 0.5 ms
(Tslot=15360Ts). Ts is a sampling time given as Ts=1/(15
kHz.times.2048)=3.2552.times.10-8 (about 33 ns).
A type-2 frame includes a special subframe having three fields,
Downlink Pilot Time Slot (DwPTS), Guard Period (GP), and Uplink
Pilot Time Slot (UpPTS). The DwPTS is used for initial cell search,
synchronization, or channel estimation at a UE, and the UpPTS is
used for channel estimation and UL transmission synchronization
with a UE at an eNB. The GP is used to cancel UL interference
between a UL and a DL, caused by the multi-path delay of a DL
signal.
Table 1 below lists special subframe configurations (DwPTS/GP/UpPTS
lengths).
TABLE-US-00001 TABLE 1 Normal cyclic prefix in downlink Extended
cyclic prefix in downlink UpPTS UpPTS Normal Extended Normal
Extended Special subframe cyclic prefix cyclic prefix cyclic prefix
cyclic prefix configuration DwPTS in uplink in uplink DwPTS in
uplink in uplink 0 6592 T.sub.s 2192 T.sub.s 2560 T.sub.s 7680
T.sub.s 2192 T.sub.s 2560 T.sub.s 1 19760 T.sub.s 20480 T.sub.s 2
21952 T.sub.s 23040 T.sub.s 3 24144 T.sub.s 25600 T.sub.s 4 26336
T.sub.s 7680 T.sub.s 4384 T.sub.s 5120 T.sub.s 5 6592 T.sub.s 4384
T.sub.s 5120 T.sub.s 20480 T.sub.s 6 19760 T.sub.s 23040 T.sub.s 7
21952 T.sub.s -- -- -- 8 24144 T.sub.s -- -- --
FIG. 3 illustrates an exemplary structure of a DL resource grid for
the duration of one DL slot, which may be used in embodiments of
the present disclosure.
Referring to FIG. 3, a DL slot includes a plurality of OFDM symbols
in the time domain. One DL slot includes 7 OFDM symbols in the time
domain and an RB includes 12 subcarriers in the frequency domain,
to which the present disclosure is not limited.
Each element of the resource grid is referred to as a Resource
Element (RE). An RB includes 12.times.7 REs. The number of RBs in a
DL slot, NDL depends on a DL transmission bandwidth. The structure
of the uplink slot may be the same as the structure of the downlink
slot.
FIG. 4 illustrates a structure of a UL subframe which may be used
in embodiments of the present disclosure.
Referring to FIG. 4, a UL subframe may be divided into a control
region and a data region in the frequency domain. A PUCCH carrying
UCI is allocated to the control region and a PUSCH carrying user
data is allocated to the data region. To maintain a single carrier
property, a UE does not transmit a PUCCH and a PUSCH
simultaneously. A pair of RBs in a subframe are allocated to a
PUCCH for a UE. The RBs of the RB pair occupy different subcarriers
in two slots. Thus it is said that the RB pair frequency-hops over
a slot boundary.
FIG. 5 illustrates a structure of a DL subframe that may be used in
embodiments of the present disclosure.
Referring to FIG. 5, up to three OFDM symbols of a DL subframe,
starting from OFDM symbol 0 are used as a control region to which
control channels are allocated and the other OFDM symbols of the DL
subframe are used as a data region to which a PDSCH is allocated.
DL control channels defined for the 3GPP LTE system include a
Physical Control Format Indicator Channel (PCFICH), a PDCCH, and a
Physical Hybrid ARQ Indicator Channel (PHICH).
The PCFICH is transmitted in the first OFDM symbol of a subframe,
carrying information about the number of OFDM symbols used for
transmission of control channels (i.e., the size of the control
region) in the subframe. The PHICH is a response channel to a UL
transmission, delivering an HARQ ACK/NACK signal. Control
information carried on the PDCCH is called Downlink Control
Information (DCI). The DCI transports UL resource assignment
information, DL resource assignment information, or UL Transmission
(Tx) power control commands for a UE group.
1.3. Dual Connectivity
FIG. 6 is a diagram to describe the concept of dual connectivity
usable for the present invention.
Referring to FIG. 6, carrier aggregation may be performed between a
macro cell 610 and small cells 620 and 630. Namely, a macro cell
may use n carriers (where n is an arbitrary positive integer) and a
small cell may use k carriers (where k is an arbitrary positive
integer). Here, carriers of the macro cell and carriers of the
small cell may include the same random frequency carriers or the
different random frequency carriers. For example, a macro cell may
use random frequencies F1 and F2 and a small cell may use random
frequencies F2 and F3.
A random User Equipment (UE) located within the small cell coverage
may be simultaneously connected to a macro cell and a small cell
and receive services from the macro cell and the small cell
simultaneously or by Time Division Multiplexing (TDM). Through a
macro cell layer, a function (e.g., connection management,
mobility, etc.) provided in a control plane (C-plane) can be
serviced. In case of a user plane (U-plane) data path, the macro
cell, the small cell or the macro cell and the small cell may be
selected. For example, in case of real-time data like Voice over
LTE (VoLTE), transmission/reception can be performed through the
macro cell that secures mobility better than the small cell. In
case of a best effect service, a service can be received from the
small cell. A connection between the macro cell and the small cell
can be established through a backhaul. And, the backhaul may
include an ideal backhaul or a nonideal backhaul.
Moreover, in case of the macro cell and the small cell, the same
TDD or FDD systems may be configured or TDD and FDD systems may be
configured.
The concept of dual connectivity may be observed from FIG. 6. It
can be observed that the macro cell and the small cell use the same
frequency band or different frequency bands. A random UE having
dual connectivity configured therefor can be simultaneously
connected to the macro cell and the small cell. FIG. 6 shows a case
that a U-plane data path is configured with the small cell.
For clarity, the present invention mentions that a random UE
configures dual connectivity with a macro cell and a small cell.
Yet, the present invention is non-limited by cell types such as
macro, micro, pico, femto and the like. Moreover, for clarity, it
is described that a random dual-connectivity UE configures Carrier
Aggregation (CA) by setting a macro cell and a small cell to a
Primary cell (Pcell) and a Secondary cell (Scell), respectively.
And, the present invention is non-limitedly applicable to other
configurations.
Particularly, the present invention includes that a single UE
configures dual connectivity to a Long Term Evolution (LTE) system
based base station and an NR system based transmission reception
point.
2. LTE-U System
2.1 LTE-U System Configuration
Hereinafter, methods for transmitting and receiving data in a CA
environment of an LTE-A band corresponding to a licensed band and
an unlicensed band will be described. In the embodiments of the
present disclosure, an LTE-U system means an LTE system that
supports such a CA status of a licensed band and an unlicensed
band. A WiFi band or Bluetooth (BT) band may be used as the
unlicensed band. LTE-A system operating on an unlicensed band is
referred to as LAA (Licensed Assisted Access) and the LAA may
correspond to a scheme of performing data transmission/reception in
an unlicensed band using a combination with a licensed band.
FIG. 7 illustrates an example of a CA environment supported in an
LTE-U system.
Hereinafter, for convenience of description, it is assumed that a
UE is configured to perform wireless communication in each of a
licensed band and an unlicensed band by using two CCs. The methods
which will be described hereinafter may be applied to even a case
where three or more CCs are configured for a UE.
In the embodiments of the present disclosure, it is assumed that a
carrier of the licensed band may be a primary CC (PCC or PCell),
and a carrier of the unlicensed band may be a secondary CC (SCC or
SCell). However, the embodiments of the present disclosure may be
applied to even a case where a plurality of licensed bands and a
plurality of unlicensed bands are used in a carrier aggregation
method. Also, the methods suggested in the present disclosure may
be applied to even a 3GPP LTE system and another system.
In FIG. 7, one eNB supports both a licensed band and an unlicensed
band. That is, the UE may transmit and receive control information
and data through the PCC which is a licensed band, and may also
transmit and receive control information and data through the SCC
which is an unlicensed band. However, the status shown in FIG. 7 is
only example, and the embodiments of the present disclosure may be
applied to even a CA environment that one UE accesses a plurality
of eNBs.
For example, the UE may configure a macro eNB (M-eNB) and a PCell,
and may configure a small eNB (S-eNB) and an SCell. At this time,
the macro eNB and the small eNB may be connected with each other
through a backhaul network.
In the embodiments of the present disclosure, the unlicensed band
may be operated in a contention-based random access method. At this
time, the eNB that supports the unlicensed band may perform a
Carrier Sensing (CS) procedure prior to data transmission and
reception. The CS procedure determines whether a corresponding band
is reserved by another entity.
For example, the eNB of the SCell checks whether a current channel
is busy or idle. If it is determined that the corresponding band is
idle state, the eNB may transmit a scheduling grant to the UE to
allocate a resource through (E)PDCCH of the PCell in case of a
cross carrier scheduling mode and through PDCCH of the SCell in
case of a self-scheduling mode, and may try data transmission and
reception.
At this time, the eNB may configure a TxOP including N consecutive
subframes. In this case, a value of N and a use of the N subframes
may previously be notified from the eNB to the UE through higher
layer signaling through the PCell or through a physical control
channel or physical data channel.
2.2 Carrier Sensing (CS) Procedure
In embodiments of the present disclosure, a CS procedure may be
called a Clear Channel Assessment (CCA) procedure. In the CCA
procedure, it may be determined whether a channel is busy or idle
based on a predetermined CCA threshold or a CCA threshold
configured by higher-layer signaling. For example, if energy higher
than the CCA threshold is detected in an unlicensed band, SCell, it
may be determined that the channel is busy or idle. If the channel
is determined to be idle, an eNB may start signal transmission in
the SCell. This procedure may be referred to as LBT.
FIG. 8 is a view illustrating an exemplary Frame Based Equipment
(FBE) operation as one of LBT operations.
The European Telecommunication Standards Institute (ETSI)
regulation (EN 301 893 V1.7.1) defines two LBT operations, Frame
Based Equipment (FBE) and Load Based Equipment (LBE). In FBE, one
fixed frame is comprised of a channel occupancy time (e.g., 1 to 10
ms) being a time period during which a communication node
succeeding in channel access may continue transmission, and an idle
period being at least 5% of the channel occupancy time, and CCA is
defined as an operation for monitoring a channel during a CCA slot
(at least 20 .mu.s) at the end of the idle period:
A communication node periodically performs CCA on a per-fixed frame
basis. If the channel is unoccupied, the communication node
transmits data during the channel occupancy time. On the contrary,
if the channel is occupied, the communication node defers the
transmission and waits until the CCA slot of the next period.
FIG. 9 is a block diagram illustrating the FBE operation.
Referring to FIG. 9, a communication node (i.e., eNB) managing an
SCell performs CCA during a CCA slot [S910]. If the channel is idle
[S920], the communication node performs data transmission (Tx)
[S930]. If the channel is busy, the communication node waits for a
time period calculated by subtracting the CCA slot from a fixed
frame period, and then resumes CCA [S940].
The communication node transmits data during the channel occupancy
time [S950]. Upon completion of the data transmission, the
communication node waits for a time period calculated by
subtracting the CCA slot from the idle period [S960], and then
resumes CCA [S910]. If the channel is idle but the communication
node has no transmission data, the communication node waits for the
time period calculated by subtracting the CCA slot from the fixed
frame period [S940], and then resumes CCA [S910].
FIG. 10 is a view illustrating an exemplary LBE operation as one of
the LBT operations.
Referring to FIG. 10(a), in LBE, the communication node first sets
q (q.di-elect cons.{4, 5, . . . , 32}) and then performs CCA during
one CCA slot.
FIG. 10(b) is a block diagram illustrating the LBE operation. The
LBE operation will be described with reference to FIG. 10(b).
The communication node may perform CCA during a CCA slot [S1010].
If the channel is unoccupied in a first CCA slot [S1020], the
communication node may transmit data by securing a time period of
up to (13/32)q ms [1030].
On the contrary, if the channel is occupied in the first CCA slot,
the communication node selects N (N.di-elect cons.{1, 2, . . . ,
q}) arbitrarily (i.e., randomly) and stores the selected N value as
an initial count. Then, the communication node senses a channel
state on a CCA slot basis. Each time the channel is unoccupied in
one specific CCA slot, the communication node decrements the count
by 1. If the count is 0, the communication node may transmit data
by securing a time period of up to (13/32)q ms [S1040].
2.3 Discontinuous Transmission in DL
When discontinuous transmission is performed on an unlicensed
carrier having a limited maximum transmission period, the
discontinuous transmission may influence on several functions
necessary for performing an operation of LTE system. The several
functions can be supported by one or more signals transmitted at a
starting part of discontinuous LAA DL transmission. The functions
supported by the signals include such a function as AGC
configuration, channel reservation, and the like.
When a signal is transmitted by an LAA node, channel reservation
has a meaning of transmitting signals via channels, which are
occupied to transmit a signal to other nodes, after channel access
is performed via a successful LBT operation.
The functions, which are supported by one or more signals necessary
for performing an LAA operation including discontinuous DL
transmission, include a function for detecting LAA DL transmission
transmitted by a UE and a function for synchronizing frequency and
time. In this case, the requirement of the functions does not mean
that other available functions are excluded. The functions can be
supported by other methods.
2.3.1 Time and Frequency Synchronization
A design target recommended by LAA system is to support a UE to
make the UE obtain time and frequency synchronization via a
discovery signal for measuring RRM (radio resource management) and
each of reference signals included in DL transmission bursts, or a
combination thereof. The discovery signal for measuring RRM
transmitted from a serving cell can be used for obtaining coarse
time or frequency synchronization.
2.3.2 DL Transmission Timing
When a DL LAA is designed, it may follow a CA timing relation
between serving cells combined by CA, which is defined in LTE-A
system (Rel-12 or earlier), for subframe boundary adjustment. Yet,
it does not mean that a base station starts DL transmission only at
a subframe boundary. Although all OFDM symbols are unavailable in a
subframe, LAA system can support PDSCH transmission according to a
result of an LBT operation. In this case, it is required to support
transmission of control information necessary for performing the
PDSCH transmission.
2.4 Measuring and Reporting RRM
LTE-A system can transmit a discovery signal at a start point for
supporting RRM functions including a function for detecting a cell.
In this case, the discovery signal can be referred to as a
discovery reference signal (DRS). In order to support the RRM
functions for LAA, the discovery signal of the LTE-A system and
transmission/reception functions of the discovery signal can be
applied in a manner of being changed.
2.4.1 Discovery Reference Signal (DRS)
A DRS of LTE-A system is designed to support on/off operations of a
small cell. In this case, off small cells correspond to a state
that most of functions are turned off except a periodic
transmission of a DRS. DRSs are transmitted at a DRS transmission
occasion with a period of 40, 80, or 160 ms. A DMTC (discovery
measurement timing configuration) corresponds to a time period
capable of anticipating a DRS received by a UE. The DRS
transmission occasion may occur at any point in the DMTC. A UE can
anticipate that a DRS is continuously transmitted from a cell
allocated to the UE with a corresponding interval.
If a DRS of LTE-A system is used in LAA system, it may bring new
constraints. For example, although transmission of a DRS such as a
very short control transmission without LBT can be permitted in
several regions, a short control transmission without LBT is not
permitted in other several regions. Hence, a DRS transmission in
the LAA system may become a target of LBT.
When a DRS is transmitted, if LBT is applied to the DRS, similar to
a DRS transmitted in LTE-A system, the DRS may not be transmitted
by a periodic scheme. In particular, it may consider two schemes
described in the following to transmit a DRS in the LAA system.
As a first scheme, a DRS is transmitted at a fixed position only in
a DMTC configured on the basis of a condition of LBT.
As a second scheme, a DRS transmission is permitted at one or more
different time positions in a DMTC configured on the basis of a
condition of LBT.
As a different aspect of the second scheme, the number of time
positions can be restricted to one time position in a subframe. If
it is more profitable, DRS transmission can be permitted at the
outside of a configured DMTC as well as DRS transmission performed
in the DMTC.
FIG. 11 is a diagram for explaining DRS transmission methods
supported by LAA system.
Referring to FIG. 11, the upper part of FIG. 11 shows the
aforementioned first scheme for transmitting a DRS and the bottom
part of FIG. 11 shows the aforementioned second scheme for
transmitting a DRS. In particular, in case of the first scheme, a
UE can receive a DRS at a position determined in a DMTC period
only. On the contrary, in case of the second scheme, a UE can
receive a DRS at a random position in a DMTC period.
In LTE-A system, when a UE performs RRM measurement based on DRS
transmission, the UE can perform single RRM measurement based on a
plurality of DRS occasions. In case of using a DRS in LAA system,
due to the constraint of LBT, it is difficult to guarantee that the
DRS is transmitted at a specific position. Even though a DRS is not
actually transmitted from a base station, if a UE assumes that the
DRS exists, quality of an RRM measurement result reported by the UE
can be deteriorated. Hence, when LAA DRS is designed, it is
necessary to permit the existence of a DRS to be detected in a
single DRS occasion. By doing so, it may be able to make the UE
combine the existence of the DRS with RRM measurement, which is
performed on successfully detected DRS occasions only.
Signals including a DRS do not guarantee DRS transmissions adjacent
in time. In particular, if there is no data transmission in
subframes accompanied with a DRS, there may exist OFDM symbols in
which a physical signal is not transmitted. While operating in an
unlicensed band, other nodes may sense that a corresponding channel
is in an idle state during a silence period between DRS
transmissions. In order to avoid the abovementioned problem, it is
preferable that transmission bursts including a DRS signal are
configured by adjacent OFDM symbols in which several signals are
transmitted.
2.5 Channel Access Procedure and Contention Window Adjustment
Procedure
In the following, the aforementioned channel access procedure and
the contention window adjustment procedure are explained in the
aspect of a transmission node.
FIG. 12 is a flowchart for explaining CAP and CWA.
In order for an LTE transmission node (e.g., a base station) to
operate in LAA Scell(s) corresponding to an unlicensed band cell
for DL transmission, it may initiate a channel access procedure
(CAP) [S1210].
The base station can randomly select a back-off counter N from a
contention window (CW). In this case, the N is configured by an
initial value Ninit [S1220]. The Ninit is randomly selected from
among values ranging from 0 to CW.sub.p.
Subsequently, if the back-off counter value (N) corresponds to 0
[S1222], the base station terminates the CAP and performs Tx burst
transmission including PSCH [S1224]. On the contrary, if the
back-off value is not 0, the base station reduces the back-off
counter value by 1 [S1230].
The base station checks whether or not a channel of the LAA
Scell(s) is in an idle state [S1240]. If the channel is in the idle
state, the base station checks whether or not the back-off value
corresponds to 0 [S1250]. The base station repeatedly checks
whether or not the channel is in the idle state until the back-off
value becomes 0 while reducing the back-off counter value by 1.
In the step S1240, if the channel is not in the idle state i.e., if
the channel is in a busy state, the base station checks whether or
not the channel is in the idle state during a defer duration (more
than 15 usec) longer than a slot duration (e.g., 9 usec) [S1242].
If the channel is in the idle state during the defer duration, the
base station can resume the CAP [S1244]. For example, when the
back-off counter value Ninit corresponds to 10, if the channel
state is determined as busy after the back-off counter value is
reduced to 5, the base station senses the channel during the defer
duration and determines whether or not the channel is in the idle
state. In this case, if the channel is in the idle state during the
defer duration, the base station performs the CAP again from the
back-off counter value 5 (or, from the back-off counter value 4 by
reducing the value by 1) rather than configures the back-off
counter value Ninit. On the contrary, if the channel is in the busy
state during the defer duration, the base station performs the step
S1242 again to check whether or not the channel is in the idle
state during a new defer duration.
Referring back to FIG. 12, the base station checks whether or not
the back-off counter value (N) becomes 0 [S1250]. If the back-off
counter value (N) becomes 0, the base station terminates the CAP
and may be able to transmit a Tx burst including PDSCH.
The base station can receive HARQ-ACK information from a UE in
response to the Tx burst [S1270]. The base station can adjust a CWS
(contention window size) based on the HARQ-ACK information received
from the UE [S1280].
In the step S1280, as a method of adjusting the CWS, the base
station can adjust the CWS based on HARQ-ACK information on a first
subframe of a most recently transmitted Tx burst (i.e., a start
subframe of the Tx burst).
In this case, the base station can set an initial CW to each
priority class before the CWP is performed. Subsequently, if a
probability that HARQ-ACK values corresponding to PDSCH transmitted
in a reference subframe are determined as NACK is equal to or
greater than 80%, the base station increases CW values set to each
priority class to a next higher priority.
In the step S1260, PDSCH can be assigned by a self-carrier
scheduling scheme or a cross-carrier scheduling scheme. If the
PDSCH is assigned by the self-carrier scheduling scheme, the base
station counts DTX, NACK/DTX, or ANY state among the HARQ-ACK
information fed back by the UE as NACK. If the PDSCH is assigned by
the cross-carrier scheduling scheme, the base station counts the
NACK/DTX and the ANY states as NACK and does not count the DTX
state as NACK among the HARQ-ACK information fed back by the
UE.
If bundling is performed over M (M>=2) number of subframes and
bundled HARQ-ACK information is received, the base station may
consider the bundled HARQ-ACK information as M number of HARQ-ACK
responses. In this case, it is preferable that a reference subframe
is included in the M number of bundled subframes.
2.6. Channel Access Priory Class
TABLE-US-00002 TABLE 2 Channel Access Priority Class (P) m.sub.p
CW.sub.min,p CW.sub.max,p T.sub.m cot,p allowed CW.sub.p sizes 1 1
3 7 2 ms {3, 7} 2 1 7 15 3 ms {7, 15} 3 3 15 63 8 or 10 ms {15, 31,
63} 4 7 15 1023 8 or 10 ms {15, 31, 63, 127, 255, 511, 1023}
As shown in Table 2, in Rel-13 LAA system, 4 channel access
priority classes are defined in total. And, a length of a defer
period, a CWS, MCOT (maximum channel occupancy time), and the like
are defined according to each of the channel access priority
classes. Hence, when an eNB transmits a downlink signal via an
unlicensed band, the eNB performs random backoff by utilizing LBT
parameters determined according to a channel access priority class
and may be then able to access a channel during limited maximum
transmission time only after the random backoff is completed.
For example, in case of the channel access priority class 1/2/3/4,
the maximum channel occupancy time (MCOT) is determined by 2/3/8/8
ms. The maximum channel occupancy time (MCOT) is determined by
2/3/10/10 ms in environment where other RAT such as Wi-Fi does not
exists (e.g., by level of regulation).
As shown in Table 2, a set of CWSs capable of being configured
according to a class is defined. One of points different from Wi-Fi
system is in that a different backoff counter value is not defined
according to a channel access priority class and LBT is performed
using a single backoff counter value (this is referred to as single
engine LBT).
For example, when an eNB intends to access a channel via an LBT
operation of class 3, since CWmin (=15) is configured as an initial
CWS, the eNB performs random backoff by randomly selecting an
integer from among numbers ranging from 0 to 15. If a backoff
counter value becomes 0, the eNB starts DL Tx and randomly selects
a new backoff counter for a next Tx burst after the DL Tx burst is
completed. In this case, if an event for increasing a CWS is
triggered, the eNB increases a size of the CWS to 31 corresponding
to a next size, randomly selects an integer from among numbers
ranging from 0 to 31, and performs random backoff.
In this case, when a CWS of the class 3 is increased, CWSs of all
classes are increased as well. In particular, if the CW of the
class 3 becomes 31, a CWS of a class 1/2/4 becomes 7/15/31. If an
event for decreasing a CWS is triggered, CWS values of all classes
are initialized by CWmin irrespective of a CWS value of the
triggering timing.
2.7. Subframe Structure Applicable to LAA System
FIG. 13 is a diagram illustrating a partial TTI or a partial
subframe applicable to the present invention.
In Rel-13 LAA system, MCOT is utilized as much as possible when DL
Tx burst is transmitted. In order to support consecutive
transmission, a partial TTI, which is defined as DwPTS, is
introduced. The partial TTI (or partial subframe) corresponds to a
section in which a signal is transmitted as much as a length
shorter than a legacy TTI (e.g., 1 ms) when PDSCH is
transmitted.
In the present invention, for clarity, a starting partial TTI or a
starting partial subframe corresponds to a form that a part of
symbols positioned at the fore part of a subframe are emptied out.
An ending partial TTI or an ending partial subframe corresponds to
a form that a part of symbols positioned at the rear part of a
subframe are emptied out. (On the contrary, an intact TTI is
referred to as a normal TTI or a full TTI.)
FIG. 13 illustrates various types of the aforementioned partial
TTI. The first drawing of FIG. 13 illustrates an ending partial TTI
(or subframe) and the second drawing illustrates a starting partial
TTI (or subframe). The third drawing of FIG. 13 illustrates a
partial TTI (or subframe) that a part of symbols positioned at the
fore part and the rear part of a subframe are emptied out. In this
case, when signal transmission is excluded from a normal TTI, a
time section during which the signal transmission is excluded is
referred to as a transmission gap (TX gap).
Although the present invention is explained on the basis of a DL
operation in FIG. 13, the present invention can also be identically
applied to a UL operation. For example, a partial TTI structure
shown in FIG. 13 can be applied to a form of transmitting PUCCH or
PUSCH as well.
3. New Radio Access Technology System
As more and more communication devices require greater
communication capacity, there is a need for mobile broadband
communication enhanced over existing radio access technology (RAT).
In addition, massive Machine-Type Communications (MTC) capable of
providing a variety of services anywhere and anytime by connecting
multiple devices and objects is also considered. Communication
system design considering services/UEs sensitive to reliability and
latency is also under discussion.
As such, introduction of new radio access technology considering
enhanced mobile broadband communication, massive MTC, and
Ultra-Reliable and Low Latency Communication (URLLC) is being
discussed. In the present invention, for simplicity, this
technology will be referred to as NewRAT or NR (New Radio).
3.1. Self-Contained Subframe Structure
FIG. 14 is a diagram illustrating a self-contained subframe
structure applicable to the present invention.
In the NR system to which the present invention is applicable, a
self-contained subframe structure as shown in FIG. 14 is proposed
in order to minimize data transmission latency in the TDD
system.
In FIG. 14, the hatched region (e.g., symbol index=0) represents a
downlink control region, and the black region (e.g., symbol
index=13) represents an uplink control region. The other region
(e.g., symbol index=1 to 12) may be used for downlink data
transmission or for uplink data transmission.
In this structure, DL transmission and UL transmission may be
sequentially performed in one subframe. In addition, DL data may be
transmitted and received in one subframe and UL ACK/NACK therefor
may be transmitted and received in the same subframe. As a result,
this structure may reduce time taken to retransmit data when a data
transmission error occurs, thereby minimizing the latency of final
data transmission.
In such a self-contained subframe structure, a time gap having a
certain temporal length is required in order for the base station
and the UE to switch from the transmission mode to the reception
mode or from the reception mode to the transmission mode. To this
end, some OFDM symbols at the time of switching from DL to UL in
the self-contained subframe structure may be set as a guard period
(GP).
While a case where the self-contained subframe structure includes
both the DL control region and the UL control region has been
described above, the control regions may be selectively included in
the self-contained subframe structure. In other words, the
self-contained subframe structure according to the present
invention may include not only the case of including both the DL
control region and the UL control region but also the case of
including either the DL control region or the UL control region
alone, as shown in FIG. 14.
For simplicity of explanation, the frame structure configured as
above is referred to as a subframe, but this configuration can also
be referred to as a frame or a slot. For example, in the NR system,
one unit consisting of a plurality of symbols may be referred to as
a slot. In the following description, a subframe or a frame may be
replaced with the slot described above.
3.2. OFDM Numerology
The NR system uses the OFDM transmission scheme or a similar
transmission scheme. Here, the NR system may typically have the
OFDM numerology as shown in Table 3.
TABLE-US-00003 TABLE 3 Parameter Value Subcarrier-spacing
(.DELTA.f) 75 kHz OFDM symbol length 13.33 us Cyclic Prefix (CP)
length 1.04 us/0.94 us System BW 100 MHz No. of available
subcarriers 1200 Subframe length 0.2 ms Number of OFDM symbol per
Subframe 14 symbols
Alternatively, the NR system may use the OFDM transmission scheme
or a similar transmission scheme, and may use an OFDM numerology
selected from among multiple OFDM numerologies as shown in Table 4.
Specifically, as disclosed in Table 4, the NR system may take the
15 kHz subcarrier-spacing used in the LTE system as a base, and use
an OFDM numerology having subcarrier-spacing of 30, 60, and 120
kHz, which are multiples of the 15 kHz subcarrier-spacing.
In this case, the cyclic prefix, the system bandwidth (BW) and the
number of available subcarriers disclosed in Table 4 are merely an
example that is applicable to the NR system according to the
present invention, and the values thereof may depend on the
implementation method. Typically, for the 60 kHz
subcarrier-spacing, the system bandwidth may be set to 100 MHz. In
this case, the number of available subcarriers may be greater than
1500 and less than 1666. Also, the subframe length and the number
of OFDM symbols per subframe disclosed in Table 4 are merely an
example that is applicable to the NR system according to the
present invention, and the values thereof may depend on the
implementation method.
TABLE-US-00004 TABLE 4 Parameter Value Value Value Value
Subcarrier- 15 kHz 30 kHz 60 kHz 120 kHz spacing (.DELTA.f) OFDM
symbol 66.66 33.33 16.66 8.33 length Cyclic 5.20 us/4.69 us 2.60
us/2.34 us 1.30 us/1.17 us 0.65 us/0.59 us Prefix (CP) length
System BW 20 MHz 40 MHz 80 MHz 160 MHz No. of available 1200 1200
1200 1200 subcarriers Subframe 1 ms 0.5 ms 0.25 ms 0.125 ms length
Number of 14 symbols 14 symbols 14 symbols 14 symbols OFDM symbol
per Subframe
3.3. Analog Beamforming
In a millimeter wave (mmW) system, since a wavelength is short, a
plurality of antenna elements can be installed in the same area.
That is, considering that the wavelength at 30 GHz band is 1 cm, a
total of 100 antenna elements can be installed in a 5*5 cm panel at
intervals of 0.5 lambda (wavelength) in the case of a 2-dimensional
array. Therefore, in the mmW system, it is possible to improve the
coverage or throughput by increasing the beamforming (BF) gain
using multiple antenna elements.
In this case, each antenna element can include a transceiver unit
(TXRU) to enable adjustment of transmit power and phase per antenna
element. By doing so, each antenna element can perform independent
beamforming per frequency resource.
However, installing TXRUs in all of the about 100 antenna elements
is less feasible in terms of cost. Therefore, a method of mapping a
plurality of antenna elements to one TXRU and adjusting the
direction of a beam using an analog phase shifter has been
considered. However, this method is disadvantageous in that
frequency selective beamforming is impossible because only one beam
direction is generated over the full band.
To solve this problem, as an intermediate form of digital BF and
analog BF, hybrid BF with B TXRUs that are fewer than Q antenna
elements can be considered. In the case of the hybrid BF, the
number of beam directions that can be transmitted at the same time
is limited to B or less, which depends on how B TXRUs and Q antenna
elements are connected.
FIGS. 15 and 16 are diagrams illustrating representative methods
for connecting TXRUs to antenna elements. Here, the TXRU
virtualization model represents the relationship between TXRU
output signals and antenna element output signals.
FIG. 15 shows a method for connecting TXRUs to sub-arrays. In FIG.
15, one antenna element is connected to one TXRU.
Meanwhile, FIG. 16 shows a method for connecting all TXRUs to all
antenna elements. In FIG. 16, all antenna element are connected to
all TXRUs. In this case, separate addition units are required to
connect all antenna elements to all TXRUs as shown in FIG. 16.
In FIGS. 15 and 16, W indicates a phase vector weighted by an
analog phase shifter. That is, W is a major parameter determining
the direction of the analog beamforming. In this case, the mapping
relationship between CSI-RS antenna ports and TXRUs may be 1:1 or
1-to-many.
The configuration shown in FIG. 15 has a disadvantage in that it is
difficult to achieve beamforming focusing but has an advantage in
that all antennas can be configured at low cost.
On the contrary, the configuration shown in FIG. 16 is advantageous
in that beamforming focusing can be easily achieved. However, since
all antenna elements are connected to the TXRU, it has a
disadvantage of high cost.
4. Proposed Embodiments
According to the present invention, operating methods of a base
station/user equipment on an unlicensed band in a Dual Connectivity
(hereinafter DC) situation (e.g., LBT method, PDCCH search space
configuring method, etc.) are described in detail based on the
above-described technology configurations.
Recently, for data offloading of an area of a hotspot (i.e.,
wireless LAN base station relaying a radio wave to use high-speed
wireless internet), a small cell is introduced into a wireless
communication system. Here, a UE can be associated with a macro
cell having a large coverage for mobility management and
additionally associated with a small cell for throughput
enhancement.
In this case, if a backhaul between the macro cell and the small
cell is ideal, the UE can receive services from both of the two
cells through Carrier Aggregation (CA) that secures inter-cell
synchronization within a predetermined level. Yet, due to the
actual deployment, the macro cell and the small cell are
geographically spaced apart from each other and may be connected to
each other nonideally, whereby standardization of Dual Connectivity
(DC) technology in LTE Release-12 system is in progress in
consideration of such a situation.
Here, one of two eNBs connected together through a nonideal
backhaul can be named a Master eNB (MeNB) and the other can be
named a Secondary eNB (SeNB). In this case, a cell group
administered by the MeNB is defined as a Master Cell Group (MCG)
and a cell group adminstered by the SeNB is defined as a Secondary
Cell Group (SCG). Moreover, for cells belonging to the MCG and
cells belonging to the SCG, CA can be configured with a cell within
each of the cell groups. A specific cell of the MCG can be
configured as a Primary Cell (PCell) and a specific cell of the SCG
can be configured as a Primary Secondary Cell (PSCell). In this
case, PUCCH and contention-based PRACH may be allowed to be
transmitted through the PCell and the PSCell.
FIG. 17 and FIG. 18 are diagrams showing dual connectivity
configurations including unlicensed component carriers applicable
to the present invention.
Thus, as deployment scenarios for DC including unlicensed component
carriers according to the present invention, two scenarios shown in
FIG. 17 and FIG. 18 can be considered.
First of all, according to one example of the present invention, as
shown in FIG. 17, it is able to consider a deployment scenario
configured with MCG including Licensed cell (L-cell) and SCG
including Unlicensed cell (U-cell) only. Secondly, according to
another example of the present invention, as shown in FIG. 18, it
is able to consider a deployment scenario configured with MCG
including L-cell and U-cell and SCG including U-cell only.
Regarding the two scenarios, if U-cell is included in SCG only,
specific U-cell in the SCG can be configured as PSCell. Yet, if
L-cell(s) is included in SCG as well as U-cell, there may be
limitation that only L-cell in the SCG can be configured as PSCell
instead of U-cell.
Moreover, in case of FIG. 18, since U-cells typically belong to
another group, they may belong to different Timing Advance Groups
(TAGs) between U-cells. Or, different U-cells may belong to
different TAGs due to a propagation delay difference according to
an inter-cell geographical location despite not belonging to
another CG.
Particularly, in case of FIG. 18, it may include a configuration
that CC #1 and CC #3 are co-located. Hence, CC #2 and CC #3 may
belong to different TAGs, respectively.
Therefore, according to the present invention, proposed is an
unlicensed component carrier operating method (e.g., LBT method,
PDCCH search space configuring method, etc.) in a dual connectivity
situation. Particularly, the present invention non-limits wireless
communication systems (e.g., LTE system, NR system, etc.) to which
the corresponding technology is applicable, and the corresponding
technology is applicable to all the various wireless communication
systems. Hence, an eNB in the following technical configuration may
be substituted with a new generation NodeB (gNB) of an NR
system.
4.1 LBT Method
In UL transmissions on two U-cells belonging to different TAGs in
aspect of a specific UE, a UL transmission to a specific U-cell may
limit a UL transmission of another U-cell due to different UL
timings.
FIG. 19 is a diagram schematically showing a subframe structure per
cell in aspect of a specific UE for two cells belonging to
different TAGs.
Referring to FIG. 19, a UE is communicating with unlicensed
component carriers CC #1 and CC #2. And, the CC #1 and CC #2 may be
configured to belong to different TAGs, respectively. Here, as the
UE succeeds in LBT for a UL transmission in SF #B, if the UE starts
a UL transmission from a subframe boundary of the SF #B, since the
UE becomes unable to attempt LBT for a UL transmission in SF #2
(due to single Radio Frequency (RF) implementation or
self-interference), the UE may not be able to perform the UL
transmission in SF #2.
To solve such a problem, the present invention proposes a following
method. First of all, transmission start points of SF #2 and SF #B
are adjusted (aligned) into the same timing (with reference to CC
#1). If a UE succeeds in LBT at the corresponding timing, the UE
starts a UL transmission scheduled in SF #B, transmits an initial
signal between the corresponding timing and a transmission start
point of SF #2, and then starts a scheduled UL transmission from
the transmission start point of SF #2.
Here, the initial signal may include a preset signal (e.g.,
DeModulation Reference Signal (DM-RS), Sounding Reference Signal
(SRS), etc.) or a copy of a UL signal to be transmitted in a next
subframe on a corresponding unlicensed component carrier.
Additionally, according to the present invention, when a UE adjusts
a transmission start point and performs LBT, a CC that becomes a
reference of the transmission start point may be changed depending
on cases. For example, if a UE fails in LBT for SF #B in the
example of FIG. 19, the UE may adjust transmission start points of
SF #2 and SF #C with reference to CC #2 and then perform LBT.
Additionally, an LBT method applicable to DL transmission of an eNB
is described as follows.
When an eNB performs a DL transmission on U-cell that is PSCell,
Random Access Response [RAR, i.e., PDCCH Cyclic Redundancy Check
(CRC) scrambled with Random Access-Radio Network Temporary
Identifier (RA-RNTI) and PDSCH including RAR Medium Access Control
(MAC) Control Element (CE) corresponding thereto] and/or Transmit
Power Control (TPC) command (i.e., PDCCH CRC scrambled with
TPC-PUSCH-RNTI and/or TPC-PUCCH-RNTI) may be included in the
corresponding DL transmission only. Here, as an LBT method
performed by the eNB before performing the corresponding DL
transmission, a rule may be configured in a manner that CCA based
LBT for a predetermined time interval (e.g., 25 .mu.sec) (or
transmission without LBT) is applied instead of category-4 based
LBT (i.e., random backoff based LBT or channel access procedure for
DL transmission including PDSCH).
Or, when an eNB performs a DL transmission on U-cell that is
PSCell, if RAR and/or TPC command is included in the corresponding
DL transmission only, although category-4 based LBT is set as an
LBT method performed by the eNB before performing the corresponding
DL transmission, the eNB can perform LBT using LBT parameters
corresponding to a specific channel access priority class (e.g.,
priority class 1). So to speak, when an eNB performs DL
transmission on U-cell that is PSCell, if RAR and/or TPC command is
included in the corresponding DL transmission only, the
corresponding eNB can be configured to perform LBT using LBT
parameters corresponding to a prescribed one (e.g., priority class
1) of a plurality of channel access priority classes. Here, the
prescribed channel access priority class may be set in advance or
by separate signaling.
4.2. PDCCH Search Space Configuring Method
According to TS 36.123 spec. document of LTE Release-14 system, the
number of PDCCH Blind Decoding (BD) candidates a UE should monitor
is defined as the following table.
TABLE-US-00005 TABLE 5 Search space S.sub.k.sup.(L) Number of PDCCH
Type Aggregation level L Size [in CCEs] candidates M.sup.(L)
UE-specific 1 6 6 2 12 6 4 8 2 8 16 2 Common 4 16 4 8 16 2
Particularly, when PDCCH is transmitted on U-cell that is PSCell,
in order for a UE to receive the PDCCH correctly, in case of U-cell
that is the PSCell, it is necessary to configure a common search
space. In this case, the PDCCH candidate numbers for Aggregation
Levels (ALs) 4 and 8 are 4 and 2, respectively. Since the UE should
perform BD on each of DCI format 1A and DCI format 1C, the UE
should perform BDs as many as total [(4+2)*2] times.
In addition thereto, in LTE Release-13 LAA system, Common PDCCH
(C-PDCCH) (here, the C-PDCCH is CRC scrambled with CC-RNTI) is
additionally introduced for the purpose of indicating a next
subframe or the number of OFDM symbols configuring the next
subframe. Here, the common PDCCH may have the same size of DCI
format 1C and include one of aggregation level 4 and aggregation
level 8. Moreover, for the common PDCCH, Control Channel Element
(CCE) index is fixed to 0.about.3 or 0.about.7. A region carrying
the corresponding PDCCH is identical to a first PDCCH candidate of
AL 4/8 of a common search space.
Accordingly, in case of configuring a PDCCH search space for U-cell
that is PSCell, it is necessary to consider a search space
corresponding to the C-PDCCH in addition to a search space defined
in the existing LTE system. Therefore, the present invention
proposes a method of configuring a PDCCH search space according to
the introduction of the C-PDCCH.
4.2.1. First PDCCH Search Space Configuring Method
As a method of making it equal to L-cell P(S)Cell in aspect of
PDCCH BD count for a common search space, it is able to decrease
the PDCCH BD number for a common search space of U-cell PSCell in
consideration of C-PDCCH having the same size of DCI format 1C. For
example, it is able to reduce the PDCCH BD number corresponding to
AL 4/8 of a common search space to 3/1. Or, while the PDCCH BD
number corresponding to DCI format 1A in the PDCCH BD number
corresponding to AL 4/8 of the common search space is maintained as
4/2, the PDCCH BD number corresponding to DCI format 1C can be
reduced to 3/1.
4.2.2. Second PDCCH Search Space Configuring Method
As another method, a method of configuring a common search space
differently is proposed. The corresponding method can solve a
problem that the number of PDCCH candidates transmittable on a
common search space is reduced due to the blocking of C-PDCCH
transmission.
Here, an offset value, which is set in advance (or by higher layer
signaling or L1 signaling) is applicable between a start CCE index
of C-PDCCH and a CCE index of a common search space.
For example, in case of AL 4, C-PDCCH may be configured with CCE
index #0/1/2/3 and a CCE index of a common search space may be
configured with #4/5/6/7, #8/9/10/11, #12/13/14/15, and
#16/17/18/19.
In addition, the second PDCCH search space configuring method may
additionally include the aforementioned first PDCCH search space
configuring method. Namely, the PDCCH BD number corresponding to AL
4/8 of a common search space can be reduced to 3/1 and an offset
value, which is set in advance (or by higher layer signaling or L1
signaling), is also applicable between a start CCE index of C-PDCCH
and a CCE index of the common search space.
For example, in case of AL 4, C-PDCCH may be configured with CCE
index #0/1/2/3 and a CCE index of a common search space may be
configured with #4/5/6/7, #8/9/10/11, and #12/13/14/15.
4.2.3. Third PDCCH Search Space Configuring Method
As another method, considering that a transmission opportunity of
RAR, TPC command of the like that will be transmitted through a
common search space (transmitted on PSCell of an existing LTE
system) due to C-PDCCH transmission, the PDCCH BD number in a
common search space may be increased. So to speak, a method of
increasing a search space for performing PDCCH BD on a common
search space is proposed.
For example, it is able to increase the PDCCH BD number
corresponding to AL 4/8 of a common search space to 5/3. Or, while
the PDCCH BD number corresponding to DCI format 1A in the PDCCH BD
number corresponding to AL 4/8 of the common search space is
maintained as 4/2, the PDCCH BD number corresponding to DCI format
1C can be increased to 5/3.
Additionally, in LTE Release-14 eLAA system, new DCI format
0A/0B/4A/4B is introduced instead of DCI format 0/4. Here, DCI
format 0A/0B can be used for the usage of 1 Transmission Block (TB)
scheduling and DCI format 4A/4B can be used for the usage of 2 TB
scheduling. DCI format 0A/4A can be utilized for the usage of
scheduling a single UL subframe only and DCI format 0B/4B can be
utilized for the usage of scheduling up to maximum 4 UL subframes
at a time.
Here, DCI format 0A/0B/4A/4B (or, some of them) can be transmitted
through the common search space. Typically, among the DCI formats
for the UL scheduling, DCI format 1A and/or DCI format having the
same size of DCI format 1C may allowed to be transmitted through
the common search space.
4.3. Half Duplex Operation
As shown in FIG. 18, in case that CC #2 that is U-cell belongs to
SCG and CC #3 that is U-cell belongs to MCG, it is assumed that
there exists a UE for which CC #3 and CC #2 are configured. Here,
considering nonideal backhaul connection between an SeNB
administering CC #2 and an MeNB administering CC #2, if DL/UL
configuration information per subframe is not shared between eNBs,
it may cause a problem.
FIG. 20 is a diagram schematically showing a case that a boundary
of DL/UL subframe structure for different cells is not aligned.
First of all, regarding a frame structure type 3 introduced for
U-cell, unlike Time Division Duplex (TDD) having the existing frame
structure type applied thereto, DL/UL configuration in a radio
frame unit is not configured by Radio Resource Control (RRC)
signaling (or cell-common L1 signaling) but DL/UL configuration is
determined dynamically according to the scheduling of eNB.
Moreover, the typical UE implementation of 5-GHz unlicensed band
follows the single RF based implementation. Hence, it is difficult
for an MeNB to be aware of DL/UL configuration of CC #2 and it is
difficult for an SeNB to be aware of DL/UL configuration of CC #3.
Here, for two subframes (e.g., SF #1 and SF #B in FIG. 20) having
an overlapping subframe boundary inbetween in aspect of a
corresponding UE, if a DL reception is scheduled for one (e.g., SF
#1) and a UL transmission is scheduled for the other (e.g., SF #B),
one (e.g., SF #B, because the DL reception from SF #1 is already in
progress) of the two subframes cannot follow the scheduling
information.
To solve such a problem, DL/UL subframe configuration information
of each eNB can be transceived between the MeNB and the SeNB (by
higher layer signaling). Here, the DL/UL subframe configuration
information may include per-subframe DL/UL(/none) and/or subframe
length information of each eNB in a specific time unit (e.g., 10
msec).
In this case, UL information included in the DL/UL subframe
configuration information may include up to information indicating
which UE is actually scheduled.
Or, the DL/UL subframe configuration information may be configured
in a manner of not including DL scheduling information but
including UL scheduling information. In this case, the DL/UL
subframe configuration information may also include up to
information indicating which UE is actually scheduled.
Hence, DL scheduling may be regarded as available for a subframe
not indicated by UL scheduling of another eNB. Or, although UL
scheduling of another eNB for a specific subframe is indicated, DL
scheduling may be regarded as available for the corresponding
subframe with respect to an actually unscheduled UE.
FIG. 21 is a diagram showing configuration of a UE and base station
for implementing the proposed embodiments.
Referring to FIG. 21, a UE according to the present invention can
perform the following method to transmit an uplink signal through a
plurality of unlicensed Component Carriers (CCs) including two or
more unlicensed CCs belonging to different TAGs (or TAGs having
different TA values).
First of all, the UE determines a start point of a foremost
subframe in a time domain with reference to a specific timing among
subframes on a plurality of the unlicensed CCs as a transmission
start point [S2110].
For example, in FIG. 19, if a UE attempts a UL transmission in SF
#B of CC #1 of U-cell and SF #2 of CC #2, the UE can determine a
start point of a foremost subframe (e.g., SF #B in FIG. 19) in a
time dimension among subframes on a plurality of unlicensed CCs
with reference to a timing of attempting the UL transmission as a
transmission start point.
Thus, the specific timing may include a timing at which the UE
attempts a scheduled UL signal transmission on a plurality of the
unlicensed CCs.
Subsequently, the UE performs a channel access procedure (e.g.,
LBT) on a plurality of the unlicensed CCs with reference to the
transmission start point [S2120].
In doing so, depending on a success or failure in the channel
access procedure of the UE [S2130]. A next operation of the UE may
vary. Particularly, depending on the success or failure in the
channel access procedure, the UE may perform a UL signal
transmission on a plurality of the unlicensed CCs from the
transmission start point [S2410] or newly perform an operation
according to the steps S2110 to S2130.
Thus, if the UE performs the operation again according to the steps
S2110 to S2130 depending on the success or failure of the channel
access procedure in the step S21320, the aforementioned specific
timing may include a timing at which the UE fails in a channel
access procedure performed in advance for the scheduled UL signal
transmission on a plurality of the unlicensed CCs.
In a step S2140, the UE may transmit a UL signal on a plurality of
the unlicensed CCs from a transmission start point corresponding to
the successful channel access procedure.
Particularly, in the step S2140, the UE may transmit an initial
signal from the transmission start point to a start point of a
subframe per unlicensed CC and then transmit a UL signal scheduled
per unlicensed CC from the start point of the subframe per
unlicensed CC after the transmission start point.
For example in detail, if the UE succeeds in the channel access
procedure for the SF #B of FIG. 19 in the step S2130, the UE may
transmit UL signals on CC #1 and CC #2 with reference to the start
point of the SF #B by different methods, respectively.
First of all, in case of CC #1, since the transmission start point
corresponding to the successful channel access procedure matches
the start point of SF #B, the UE can transmit a UL signal scheduled
for the CC #1 from the start point (or the transmission start
point) of the SF #B. On the other hand, in case of CC #2, since the
transmission start point corresponding to the successful channel
access procedure is ahead of the start point of SF #2, the UE may
transmit an initial signal on CC #2 from the transmission start
point to the start point of the SF #2 and then transmit a UL signal
scheduled for the CC #2 on the CC #2 after the start point of the
SF #2.
In doing so, the initial signal may include a signal configured in
advance on a system or a portion or whole of a UL signal to be
transmitted thereafter. According to one example shown in FIG. 19,
the initial signal may include a portion or whole of a UL signal
scheduled in SF #3 on CC #2 or a signal configured in advance on a
system.
According to the present invention, two or more unlicensed CCs
belonging to different TAGs may be connected to the UE on a manner
of (or by) dual connectivity.
As examples of the above-described proposed methods can be included
in the implementing methods of the present invention, they can be
obviously regarded as a sort of proposed methods. Moreover,
although the above-described proposed methods can be implemented
independently, they may be implemented in a manner of combination
(or aggregation) of some proposed methods. And, a rule may be
defined in a manner that a base station informs a user equipment
whether the proposed methods are applied (or information on rules
of the proposed methods) through a predefined signal (e.g.,
physical layer signal or higher layer signal).
5. Device Configuration
FIG. 22 is a diagram illustrating configurations of a UE and a base
station capable of being implemented by the embodiments proposed in
the present invention. The UE shown in FIG. 22 operate to implement
the embodiments of the method for transmitting an uplink
signal.
A UE 1 may act as a transmission end on a UL and as a reception end
on a DL. A base station (eNB or gNB) 100 may act as a reception end
on a UL and as a transmission end on a DL.
That is, each of the UE and the base station may include a
Transmitter (Tx) 10 or 110 and a Receiver (Rx) 20 or 120, for
controlling transmission and reception of information, data, and/or
messages, and an antenna 30 or 130 for transmitting and receiving
information, data, and/or messages.
Each of the UE and the base station may further include a processor
40 or 140 for implementing the afore-described embodiments of the
present disclosure and a memory 50 or 150 for temporarily or
permanently storing operations of the processor 40 or 140.
The above-configured UE 1 can transmit a UL signal through a
plurality of unlicensed Component Carriers (CCs) including two or
more unlicensed CCs belonging to different Timing Advance Groups
(TAGs), respectively.
As a method for this, the UE determines a start point of a foremost
subframe in a time domain with reference to a specific timing among
subframes on a plurality of the unlicensed CCs as a transmission
start point through the processor 40. Subsequently, the UE 1
performs a channel access procedure on a plurality of the
unlicensed CCs with reference to the transmission start point
through the processor 40 that controls the transmitter 10 and the
receiver 20. Subsequently, depending on a success or failure in the
channel access procedure, the UE 1 perform a UL signal transmission
on a plurality of the unlicensed CCs from the transmission start
point through the transmitter 10 or attempts the UL Signal
transmission by determining a new transmission start point through
the processor 40 and then performing a new channel access procedure
with reference to the new transmission start point.
The Tx and Rx of the UE and the base station may perform a packet
modulation/demodulation function for data transmission, a
high-speed packet channel coding function, OFDM packet scheduling,
TDD packet scheduling, and/or channelization. Each of the UE and
the base station of FIG. 22 may further include a low-power Radio
Frequency (RF)/Intermediate Frequency (IF) module.
Meanwhile, the UE may be any of a Personal Digital Assistant (PDA),
a cellular phone, a Personal Communication Service (PCS) phone, a
Global System for Mobile (GSM) phone, a Wideband Code Division
Multiple Access (WCDMA) phone, a Mobile Broadband System (MBS)
phone, a hand-held PC, a laptop PC, a smart phone, a Multi
Mode-Multi Band (MM-MB) terminal, etc.
The smart phone is a terminal taking the advantages of both a
mobile phone and a PDA. It incorporates the functions of a PDA,
that is, scheduling and data communications such as fax
transmission and reception and Internet connection into a mobile
phone. The MB-MM terminal refers to a terminal which has a
multi-modem chip built therein and which can operate in any of a
mobile Internet system and other mobile communication systems (e.g.
CDMA 2000, WCDMA, etc.).
Embodiments of the present disclosure may be achieved by various
means, for example, hardware, firmware, software, or a combination
thereof.
In a hardware configuration, the methods according to exemplary
embodiments of the present disclosure may be achieved by one or
more Application Specific Integrated Circuits (ASICs), Digital
Signal Processors (DSPs), Digital Signal Processing Devices
(DSPDs), Programmable Logic Devices (PLDs), Field Programmable Gate
Arrays (FPGAs), processors, controllers, microcontrollers,
microprocessors, etc.
In a firmware or software configuration, the methods according to
the embodiments of the present disclosure may be implemented in the
form of a module, a procedure, a function, etc. performing the
above-described functions or operations. A software code may be
stored in the memory 50 or 150 and executed by the processor 40 or
140. The memory is located at the interior or exterior of the
processor and may transmit and receive data to and from the
processor via various known means.
Those skilled in the art will appreciate that the present
disclosure may be carried out in other specific ways than those set
forth herein without departing from the spirit and essential
characteristics of the present disclosure. The above embodiments
are therefore to be construed in all aspects as illustrative and
not restrictive. The scope of the disclosure should be determined
by the appended claims and their legal equivalents, not by the
above description, and all changes coming within the meaning and
equivalency range of the appended claims are intended to be
embraced therein. It is obvious to those skilled in the art that
claims that are not explicitly cited in each other in the appended
claims may be presented in combination as an embodiment of the
present disclosure or included as a new claim by a subsequent
amendment after the application is filed.
INDUSTRIAL APPLICABILITY
The present disclosure is applicable to various wireless access
systems including a 3GPP system, and/or a 3GPP2 system. Besides
these wireless access systems, the embodiments of the present
disclosure are applicable to all technical fields in which the
wireless access systems find their applications. Moreover, the
proposed method can also be applied to mmWave communication using
an ultra-high frequency band.
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